This invention was made in part with funding from the United States Government, and the U.S. Government has certain rights in the invention.
This invention relates to the general fields of passive mucosal immune protection, and of poly-Ig immune reagents and techniques. We use the term poly-Ig to refer to the polymeric classes of antibodies-i.e. IgA and IgM. IgM antibodies are generally produced at an early stage of the immune response and are not an important factor in protective mucosal immunity. Thus, the invention generally refers to polymeric Ig antibodies, and the usual and preferred antibodies for all aspects of the invention are IgA class antibodies, which normally are secreted in dimeric form and, to a lesser degree, as higher IgA polymers.
Many pathogenic bacteria and viruses initially gain entry into the body by crossing the cellular linings (epithelia) of the gastrointestinal, respiratory, or genital tracts. A specialized class of antibodies, IgA antibodies, protects these surfaces. IgA antibodies are dimeric or polymeric molecules produced by cells located in the tissues under the epithelial surfaces. They are transported by epithelial cells into mucosal secretions, where they cross-link or coat pathogens that have not yet entered the body, preventing the pathogens from contacting and adhering to epithelial cells. Thus, IgA antibodies operate on pathogens that are outside the body, and they protect by preventing entry into the body across epithelial surfaces.
The naturally occurring IgA response is triggered by antigen delivery to mucosal surfaces. The antigen enters the body through specific sampling sites (termed microfold or M cells) that effect transepithelial antigen transport to areas of the mucosal lining containing specialized, organized collections of the cells of the mucosal immune system. More specifically, as shown in FIG. 1, antigens A (shown as filled dots) in lumen 1 bind the luminal surface of M cells at site 2. The antigens are internalized and transcytosed at 3 to be released in the intra-epithelial pocket 4 containing lymphoid cells L (B and T cells) and antigen-processing/presenting cells such as macrophage cells (M).
IgA antibodies in a naturally immunized host are transported into secretions by binding to a specific receptor (called the poly-Ig receptor) on the basal (interior) surfaces of epithelial and glandular cells throughout the respiratory and digestive systems, the genital tract, and the mammary glands. See Solari and Kraehenbuhl, "Receptor-Mediated Transepithelial Transport of Polymeric Immunoglobulins", pp. 269-298 in The Mammary Gland, Nelville and Daniel Eds., Plenum Publishing, Cambridge (1987); Mestecky (1987) J. Clin. Immunol. 7:265-276. Receptor-IgA complexes are transported across these cells and exocytosed onto luminal (exterior) cell surfaces where the receptor is enzymatically cleaved, releasing IgA into secretions along with a receptor fragment called secretory component (SC). See Mostov et. al. (1980) Proc. Nat'l Acad. Sci. U.S.A. 77:7257-7261; Solari, R. and Kraehenbuhl, J. P. Cell 36:61-71 (1984); Kuhn and Kraehenbuhl, J .Biol. Chem. 256:12490-12495(1981). It is reported that secretory component reduces proteolytic degradation of IgA. Lindh, J., J. Immunol. 114:284-286 (1975); Brown, Neucomb, Ishizaka, J. Clin. Invest. 49:1374 (1974).
In general, existing immunization strategies which involve injection of antigens evoke production of the IgG class of antibodies that circulate systemically and neutralize pathogens after they have entered the body. Injection of antigens does not generally evoke a substantial IgA response.
Efforts to take advantage of IgA protection at mucosal barriers involve oral immunization, either for active protection of the immunized mammal or for passive protection of another mammal using mucosal secretion of the immunized mammal. Glass et. al., New Eng. J. Med., 308:1389-1392 (1983); Fubara et. al., J. Immunol., 111(2):395-403 (1973). Monoclonal IgA antibodies have been produced and applied directly to respiratory mucosal surfaces in an effort to protect against pathogen entry. Mazanec et. al. J. Virol., 61:2624-2625 (1987).
Active immunization may involve challenge at the mucosal surface with intact (killed) bacteria or viruses. To avoid dangers that may be associated with this approach for certain pathogens, component antigens, such as immunogenic surface components of the pathogen, are applied at a mucosal surface. In some cases, the antigens have been conjugated to larger molecules. For example, the cholera toxin B subunit has been conjugated to antigens. See, Czerkinsky et. al. who report oral administration of a streptococcal antigen coupled to cholera toxin B subunit in Infection and Immunity 57:1072-1077 (1989). Biodegradable microspheres have also been used as an antigen carrier. For example, Eldridge et. al. Curr. Top. Microbial Immunol. 146:59 et. seq. (1989) report incorporation of antigen into biodegradable microspheres. The dry protein antigen is dispersed in a copolymer matrix without chemical conjugation.